1. Technical Field of the Invention
The present invention relates to a robot having a movable body which is moved along a linear movement rail horizontally extending in the X-axis direction.
2. Related Art
Some types of robots have been known, which carry out tasks, such as an assembly, in an industrial plant in which an assembly line is provided as a task line. For example, as disclosed in Japanese Patent Application Laid-Open Publication No. 8-141949, Cartesian coordinate robots (X-Y robots) have been known as a type of such robots.
Such a Cartesian coordinate robot works in a space defined by an X-axis (a linearly movable axis), a Y-axis orthogonal to the X-axis, a Z-axis (a vertical axis) orthogonal to the X- and Y-axes, and a T-axis (a rotation axis) orthogonal to the X-axis. This robot includes an X-axis transfer unit disposed on the floor of a factory, a Y-axis transfer unit moved by the X-axis transfer unit in the X-axis direction, a Z-axis transfer unit moved by the Y-axis transfer unit in the Y-axis direction, and a wrist unit moved by the Z-axis transfer unit in the vertical direction (Z-axis direction) and rotatable about the X-axis (T-axis). A task tool, such as a chuck, is attached to the wrist unit in a replaceable manner. Thus, it is so configured that a task can be performed with the wrist unit (task tool), being freely moved in the three directions defined by the X, Y and Z axes.
While the robots as described above are involved in their tasks in a task line, there has been an increasing need, for example, of gaining a good view over the factory so that one can easily grasp the operating conditions of the task line. For this reason, it has been desired to reduce the volume of a task line (i.e., an assembly line or a production line) (hereinafter the volume of a task line is referred to as a “task line volume”), or more specifically, the vertical dimension of a task line.
Accordingly, those robots which are used in a task line are also desired to be reduced in their dimensions in the vertical direction (Z-axis direction) and the widthwise direction (Y-axis direction), excepting the X-axis direction which usually coincides with the transfer direction of work, i.e. the task line, along which such robots are arranged. Of the two dimensions, the dimension in the vertical direction has particularly been desired to be reduced, in order to ensure a good view over the factory.
However, such a generally used Cartesian coordinate robot, with all of the three axes X, Y and Z being linear movement axes, will have a problem in reducing the task line volume. For example, the Z-axis transfer unit needs to have a vertical dimension suitable for the required vertical movement range of the wrist unit. However, it is difficult to achieve good reduction in the vertical dimension of the Cartesian coordinate robot if the required vertical movement range of the wrist unit is to be maintained.
Also, achieving reduction in the task line volume would be useless if the reduction causes the takt time (movement speed of the robot) to be lengthened. With the achievement of the reduction in the task line volume, at least the takt time of the conventional level is required to be maintained. In addition, it is needed to avoid obstacles on the task line or suspended overhead without causing collision with the obstacles.